hydrogen breath test

hydrogen breath test A test that uses the measurement of hydrogen in the breath to diagnose several conditions that cause gastrointestinal symptoms. Large amounts of hydrogen may be produced by anaerobic bacteria in the colon when there is a problem with the digestion or absorption of food in the small intestine that allows more unabsorbed food to reach the colon, or when the colonic bacteria move back into the small intestine. Hydrogen produced by the bacteria is absorbed into the blood and travels to the lungs where it is exhaled in the breath and measured. The diagnosis of lactose intolerance is one of the most common indications for use of a hydrogen breath test.